X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcDefaults.lhs;h=5db15376871ec9c1253b4a3477eb5e21942bb266;hb=98643c2d5bd08ec71edd555e8989e530de6f5921;hp=aaed7c2221a0bd0fbdd81e8a3878d877f785ee7d;hpb=ff755dd9a0a0ad2f106c323852553ea247f16141;p=ghc-hetmet.git

diff --git a/ghc/compiler/typecheck/TcDefaults.lhs b/ghc/compiler/typecheck/TcDefaults.lhs
index aaed7c2..5db1537 100644
--- a/ghc/compiler/typecheck/TcDefaults.lhs
+++ b/ghc/compiler/typecheck/TcDefaults.lhs
@@ -8,64 +8,60 @@ module TcDefaults ( tcDefaults ) where
 
 #include "HsVersions.h"
 
-import HsSyn		( HsDecl(..), DefaultDecl(..) )
-import RnHsSyn		( RenamedHsDecl )
-
-import TcMonad
-import TcEnv		( tcLookupClassByKey_maybe )
-import TcMonoType	( tcHsType )
-import TcSimplify	( tcSimplifyCheckThetas )
-
-import TysWiredIn	( integerTy, doubleTy )
-import Type             ( Type )
-import Unique		( numClassKey )
+import HsSyn		( DefaultDecl(..) )
+import Name		( Name )
+import TcRnMonad
+import TcEnv		( tcLookupClass )
+import TcHsType		( tcHsSigType, UserTypeCtxt( DefaultDeclCtxt ) )
+import TcSimplify	( tcSimplifyDefault )
+import TcType           ( Type, mkClassPred, isTauTy )
+import PrelNames	( numClassName )
 import Outputable
 \end{code}
 
 \begin{code}
-default_default = [integerTy, doubleTy]
-
-tcDefaults :: [RenamedHsDecl]
-	   -> TcM s [Type] 	    -- defaulting types to heave
+tcDefaults :: [DefaultDecl Name]
+	   -> TcM (Maybe [Type])    -- Defaulting types to heave
 				    -- into Tc monad for later use
 				    -- in Disambig.
-tcDefaults decls = tc_defaults [default_decl | DefD default_decl <- decls]
-
-tc_defaults [] = returnTc default_default
-
-tc_defaults [DefaultDecl [] locn]
-  = returnTc []		-- no defaults
-
-tc_defaults [DefaultDecl mono_tys locn]
-  = tcLookupClassByKey_maybe numClassKey	`thenNF_Tc` \ maybe_num ->
-    case maybe_num of {
-	Nothing -> 	-- Num has not been sucked in, so the defaults will
-			-- never be used; so simply discard the default decl.
-			-- This slightly benefits modules that don't use any
-			-- numeric stuff at all, by avoid the necessity of
-			-- always sucking in Num
-		returnTc [] ;
 
-	Just num ->	-- The common case
-
-    tcAddSrcLoc locn $
-    mapTc tcHsType mono_tys	`thenTc` \ tau_tys ->
-
-	    -- Check that all the types are instances of Num
-	    -- We only care about whether it worked or not
-    tcAddErrCtxt defaultDeclCtxt		$
-    tcSimplifyCheckThetas
-		[{- Nothing given -}]
-		[ (num, [ty]) | ty <- tau_tys ]	`thenTc_`
-
-    returnTc tau_tys
-    }
-
-tc_defaults decls@(DefaultDecl _ loc : _) =
-    tcAddSrcLoc loc $
+tcDefaults [] 
+  = getDefaultTys		-- No default declaration, so get the
+				-- default types from the envt; 
+				-- i.e. use the curent ones
+				-- (the caller will put them back there)
+	-- It's important not to return defaultDefaultTys here (which
+	-- we used to do) because in a TH program, tcDefaults [] is called
+	-- repeatedly, once for each group of declarations between top-level
+	-- splices.  We don't want to carefully set the default types in
+	-- one group, only for the next group to ignore them and install
+	-- defaultDefaultTys
+
+tcDefaults [DefaultDecl [] locn]
+  = returnM (Just [])		-- Default declaration specifying no types
+
+tcDefaults [DefaultDecl mono_tys locn]
+  = addSrcLoc locn 			$
+    addErrCtxt defaultDeclCtxt		$
+    tcLookupClass numClassName		`thenM` \ num_class ->
+    mappM tc_default_ty mono_tys	`thenM` \ tau_tys ->
+    
+    	-- Check that all the types are instances of Num
+    	-- We only care about whether it worked or not
+    tcSimplifyDefault [mkClassPred num_class [ty] | ty <- tau_tys]	`thenM_`
+    
+    returnM (Just tau_tys)
+
+tcDefaults decls@(DefaultDecl _ loc : _) =
+    addSrcLoc loc $
     failWithTc (dupDefaultDeclErr decls)
 
 
+tc_default_ty hs_ty 
+ = tcHsSigType DefaultDeclCtxt hs_ty		`thenM` \ ty ->
+   checkTc (isTauTy ty) (polyDefErr hs_ty)	`thenM_`
+   returnM ty
+
 defaultDeclCtxt =  ptext SLIT("when checking that each type in a default declaration")
 		    $$ ptext SLIT("is an instance of class Num")
 
@@ -75,5 +71,8 @@ dupDefaultDeclErr (DefaultDecl _ locn1 : dup_things)
       4  (vcat (map pp dup_things))
   where
     pp (DefaultDecl _ locn) = ptext SLIT("here was another default declaration") <+> ppr locn
+
+polyDefErr ty 
+  = hang (ptext SLIT("Illegal polymorphic type in default declaration") <> colon) 4 (ppr ty) 
 \end{code}